Allow IO to be wrapped in a newtype in foreign import/export

[ghc-hetmet.git] / compiler / typecheck / TcForeign.lhs

diff --git a/compiler/typecheck/TcForeign.lhs b/compiler/typecheck/TcForeign.lhs
index 4be039b..fc98fdb 100644 (file)
--- a/compiler/typecheck/TcForeign.lhs
+++ b/compiler/typecheck/TcForeign.lhs
@@ -35,7 +35,7 @@ import SMRep          ( argMachRep, primRepToCgRep, primRepHint )
 import OccName         ( mkForeignExportOcc )
 import Name            ( Name, NamedThing(..), mkExternalName )
 import TcType          ( Type, tcSplitFunTys, tcSplitTyConApp_maybe,
-                         tcSplitForAllTys, 
+                         tcSplitForAllTys, tcSplitIOType_maybe,
                          isFFIArgumentTy, isFFIImportResultTy, 
                          isFFIExportResultTy, isFFILabelTy,
                          isFFIExternalTy, isFFIDynArgumentTy,
@@ -277,13 +277,14 @@ nonIOok  = True
 mustBeIO = False
 
 checkForeignRes non_io_result_ok pred_res_ty ty
- = case tcSplitTyConApp_maybe ty of
-      Just (io, [res_ty]) 
-        | io `hasKey` ioTyConKey && pred_res_ty res_ty 
-       -> returnM ()
-      _   
-        -> check (non_io_result_ok && pred_res_ty ty) 
-                (illegalForeignTyErr result ty)
+       -- (IO t) is ok, and so is any newtype wrapping thereof
+  | Just (io, res_ty) <- tcSplitIOType_maybe ty,
+    pred_res_ty res_ty
+  = returnM ()
+ 
+  | otherwise
+  = check (non_io_result_ok && pred_res_ty ty) 
+         (illegalForeignTyErr result ty)
 \end{code}
 
 \begin{code}